Responsive and Responsible by Scott Jehl

February 18th, 2013

Scott is here at An Event Apart in Atlanta to talk to us about being responsibly responsive. Scott works with Filament Group on large-scale responsive designs like the Boston Globe. They’ve always focused on progressive enhancement and responsive design feels like a natural evolution of that.

But responsive design is just a small part of what goes into responsible design. Responsible design isn’t just about layout, it’s about making sure that adding advanced features doesn’t inconvenience anyone. Mostly, we need to care; we need to care about people in situations other than our own.

This became very clear to Scott when he was travelling in southeast Asia, working remotely with his colleagues back in Boston. Most of the time he was accessing the web through a USB dongle over a cellular network. That’s how most people get online there. So don’t make assumptions about screen size and bandwidth.

Browsing via this dongle was frustrating. It was frustrating for Scott because, as a developer, he knew that there was no reason for the web to be so difficult to use on this connection.

It’s our fault. The average web page is over a megabyte in size. A megabyte! That breaks down to a lot of images, plenty of JavaScript, some HTML, and “other” …which means cat pictures. Sending 800K of images is a lot for any kind of device. Same with JavaScript: 200K is a lot. The benefits that we as developers get from that JavaScript is burdening our users.

When you prototype interactions, are you thinking about your own clock …or the user’s?

The average load time for the top 200 websites is between 6 and 10 seconds on a good connection.

Good performance is good design. Scott shows a graph of “webpage loading time” on one axis against “swear words” on the other. The graph trends upwards.

Now those 1MB webpages were probably desktop-specific sites, not responsive sites. But 86% of responsive sites send the same assets to all devices.

We have to design for new sizes and new input methods, but at the same time, the old contexts aren’t going away.

We’re moving from normalisation to customisation. We used to try to make things look and work the same in every browser. It was always a silly goal, but now it seems totally ridiculous. But content parity does not require experience parity. In fact, if things look and act the same across all devices, that might mean that we’ve missed a lot of opportunities.

We should avoid presumptions. We might be able to get the dimensions of a screen, but that could be different to the dimensions of the viewport. Instead of using pixels for breakpoints, we can use ems so that the user’s font size determines the layout changes.

Before we look at some responsible techniques, let’s look at the anatomy of a page load.

HTTP

We begin with typing a URL. That request goes to a DNS server. Then the request is sent to the right host. Then the host sends a response. But on a mobile device, there’s an extra step. You have to go through a tower first, before reaching the DNS server. That connection to the tower takes two seconds (for radio). That two-second delay only happens once, thankfully.

Once the connection is made, the HTML response sends more requests: CSS, JavaScript, pictures of cats. During this time, the browser holds off on rendering. This is the critical path.

After about eight seconds, the carrier drops the connection. That two-second connection needs to be made again. So we should try to get everything during that initial eight second period.

HTML

Network conditions can change. Every HTTP request is a gamble. Say you’ve embedded a third-party widget, like Twitter’s. If you’re in a country like China that blocks Twitter, the page will never load. Chrome will hang for thirty seconds.

We need to ensure that we’re delivering assets responsibly. Consider using conditional loading. On the Boston Globe, the home page has a lot of content. The headlines certainly belong there. But content from individual sections (that you can get to from the top navigation) is also being pulled into the homepage. We definitely want to provide the link to, for example, the sports section, but the latest content from the sports section could be conditionally loaded.

CSS

Let’s look at how we deliver CSS. The way that we load CSS today is going to catch up with us. According to the HTTP Archive, the transfer size of CSS has the highest correlation to render time.

As a start, we should be using mobile-first media queries. That means starting with the styles for absolutely every device. Then we start adding our media queries for wider and wider viewport widths. This gives you a broadly-usable default. Those initial styles should go to everyone, but Scott likes to qualify them with an only all media query for some enhanced small-screen layout declarations. That makes sure that really old browsers won’t mess it up.

Generally mobile-first media queries work pretty well. But there’s a problem. We’re sending all the CSS to all the devices, even if they’ll never use half of it.

Would it be better to use multiple link elements with different media types? Alas, no. Browsers will download all stylesheets (even if the media type is set to “nonsense”) just in case they’ll need ‘em later. And unfortunately those requests are blocking. Modern WebKit browsers do a bit better. It still downloads all the stylesheets but it will render once it has the small-screen CSS.

The best approach is, unfortunately, to send just one CSS file but minify, compress, gzip and cache the shit out of it. CSS compresses really well. Gzip works by spotting redundant data—as soon as it notices a repeating segment, you get a gain. And CSS is full of repeated properties and declarations.

Images

Images are an interesting problem. Remember they were the worst offenders in page bloat. Fortunately they don’t block, but still—this problem will only get worse.

There are background images. They’re easy. Browsers have gotten very smart about only downloading the background images they need.

Foreground images aren’t so easy. There’s the compressive image technique that Luke mentioned. Make the JPEG bigger in size, but lower in quality. When it’s scaled down in the browser, it looks perfectly fine. A 1x image saved at 90% quality, it’s 95K. The same image at 2x with 0% quality is 44K.

But there’s a concern about the memory footprint of doing this on some devices. Filament Group are looking into this but it’s very hard to test.

With compressive images, you just have to point to them in one img element using the src attribute.

Responsive images are much trickier. There are two proposals.

The first is the picture element, which uses multiple source elements to specify different images for different breakpoints. There’s also a fallback image as a last resort for older browsers.

The second proposal is the srcset attribute. It’s particularly well-suited to different pixel densities. The advantage of this one is that the browser, rather than the author, gets the last say about which image should be displayed. There’s also talk about merging both proposals.

Neither proposal works today so Scott created Picturefill, a polyfill for the picture proposal, although it uses divs. The fallback image goes in a noscript element to prevent browsers from pre-fetching it.

Since picture and Picturefill work with media queries, perhaps you can default to standard definition but allow users to opt in to high definition versions.

Managing different images for different resolutions and pixel densities gets very tedious. Maybe we should abandon the pixel. Certainly for icons, SVG can be really useful. It’s well-supported today. It also compresses well, because it is text: it’s a markup language, like HTML. That means you can also edit the source of an SVG image in a text editor.

You can reference the SVG file directly in the src attribute of an img element. For older browsers, you could use onerror to replace it with a different image format.

You can also put SVG as a background image. And you use them as data-URLs and just write out the SVG in your stylesheet.

Building on that, there’s a tool called Grunticon that generates and regenerates CSS whenever you make changes to an image. It also generates a preview document for you.

JavaScript

Lastly, there’s JavaScript. The trick is to stay off the critical path. Load just as much as you need up front, so you can load more later on.

Scott uses a handful of variables to determine what needs to be loaded or not:

Broad qualification. Does the browser support “only all”? Scott uses YepNope to test and if the test comes back positive, he loads in his global JavaScript.